The present invention relates to a semiconductor light-emitting device used for optical transmission (particularly for IEEE 1394) and displays and the like.
Recently, semiconductor light-emitting devices are widely used in optical communication, information display panels, and the like. It is important that these semiconductor light-emitting devices have a high emission efficiency, and in the case of optical communication, they have additionally a high response speed particularly. Thus, in recent years, such devices are extensively developed.
Conventional surface-emitting type LEDs are not excellent in high-speed responsiveness. Their response speed is at fastest around 100 Mbpsxcx9c200 Mbps. Therefore, semiconductor light-emitting devices designated as a resonant cavity LED or a surface-emitting laser diode have been developed. These semiconductor light-emitting devices realize a high-speed response and a high efficiency by adjusting a position of an antinode in a standing wave which is generated in a resonator defined by two mirrors so as to locate at a light-emitting layer.
More recently, it has began to use plastic optical fibers (POFs) for a relatively short distance communication and, therefor, a resonant cavity LED and a surface-emitting laser diode have been developed, in which a light-emitting layer thereof is made from an AlGaInP semiconductor material capable of emitting light with a high efficiency at 650 nm in the wavelength range of a low-loss region for the POF (High Brightness Visible (660 nm) Resonant-Cavity Light-Emitting Diode, IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 10. Dec. 12, 1998.)
However, since in the conventional resonant cavity LED or surface-emitting laser diode, an active layer must be made to locate precisely at the antinode of the standing wave, such devices are fabricated to have a resonator length of around a wavelength. As the result, the distance between the active layer and a distributed Bragg reflector (DBR) on the side of the substrate is very small.
When the light-emitting layer is made from an AlGaInP material, a DBR made from an AlGaAs material is used for a DBR on the substrate side which is required to have almost 100% of reflectance. This is because that an AlGaAs material provides a greater difference in a refractive index between a layer having a higher refractive index and a layer having a lower refractive index than an AlGaInP material does when a DBR is made from a material transparent to a wavelength of 650 nm.
However, in the case of a resonant cavity-type LEDs or a surface-emitting laser diode in which the distance from an active layer to a boundary where Group V elements, As and P, are exchanged (As-by-P exchange boundary) is short, there is a problem that the internal quantum efficiency deteriorates due to poor crystal quality in the As-by-P exchange boundary. The above-mentioned problem can be also said for a usual-type LED, the internal quantum efficiency thereof deteriorates when a distance between the active layer and the As-by-P exchange boundary is below a certain value.
Thus, an object of the present invention is to provide a semiconductor light-emitting device capable of emitting light with a high efficiency by extending a distance from an active layer to a boundary where crystal quality is poor due to exchange between Group V elements As and P to suppress deterioration in crystal quality of the active layer, in order to solve the problems mentioned above.
In order to attain the object of the present invention, a semiconductor light-emitting device described in claim 1 comprises a semiconductor substrate, a plurality of reflecting multilayers, and a light-emitting layer, wherein the plurality of reflecting multilayers are formed on the semiconductor substrate by using at least two material systems having a variable refractive index, and have a lattice constant similar to that of the semiconductor substrate, each of the plurality of reflecting multilayers being made from a single material system, and the light-emitting layer is formed on the plurality of reflecting multilayers, and comprises one or more layers including an active layer made from the same material system as that of the uppermost reflecting multilayer.
In the semiconductor light-emitting device according to claim 1, a high reflectance is achieved by forming a reflecting multilayer made from a different material system from that of a light-emitting layer, while decrease in the crystal quality in the active layer is avoided by forming thereon a reflecting multilayer made from the same material system as that of the light-emitting layer and, thereafter, forming the light-emitting layer to extend a distance from a material system exchange boundary to the active layer.
A semiconductor light-emitting device described in claim 2 is characterized in that a reflecting multilayer is formed on the light-emitting layer by using a material system having a lattice constant similar to that of the light-emitting layer in the semiconductor light-emitting device according to claim 1.
In the semiconductor light-emitting device according to claim 2, since the reflecting multilayer on the light-emitting layer is made from a material system having a lattice constant similar to that of the light-emitting layer, a mirror-like state can be easily obtained, and a high reflectance can be obtained with a less number of reflecting multilayers.
The semiconductor light-emitting device described in claim 3 is characterized in that the reflecting multilayer having a lattice constant similar to that of the light-emitting layer is formed on the light-emitting layer by using the same material system as that of the light-emitting layer in the semiconductor light-emitting device according to claim 2.
In the semiconductor light-emitting device according to claim 3, since the reflecting multilayer on the light-emitting layer is made from the same material system as that of the light-emitting layer, it is more easy to fabricate the semiconductor device rather than when the reflecting multilayer on the light-emitting layer has the same lattice constant as that of the light-emitting layer and is made from a different material system from that of the light-emitting layer.
The semiconductor light-emitting device described in claim 4 is characterized in that a plurality of reflecting multilayers are formed on a light-emitting layer by using at least two material systems, each of said material systems having a variable refractive index, each of the plurality of reflecting multilayers being made from a single material system,
wherein the closest layer of the plurality of reflecting multilayers to the light-emitting layer is formed by using the same material system as that of the light-emitting layer in the semiconductor light-emitting device according to claim 3.
In the semiconductor light-emitting device according to claim 4, since reflecting multilayers made from a different material system from that of the light-emitting layer are provided above the light-emitting layer without directly contacting with the light-emitting layer, a reflectance of the reflecting multilayers above the light-emitting layer can be highten with a less number of the reflecting multilayers.
The semiconductor light-emitting device described in claim 5 is characterized in that one layer constituting a reflecting multilayer in contact with the light-emitting layer has a greater energy gap than another layer consitituting the reflecting multilayer does in the semiconductor light-emitting device according to any one of claims 1 to 4.
In the semiconductor light-emitting device according to claim 5, since the layer formed by using the material having a greater energy gap contacts the light-emitting layer, overflow of carrier can be suppressed.
The semiconductor light-emitting device described in claim 6 is characterized in that the semiconductor substrate is made from GaAs in the semiconductor light-emitting device according to any one of claims 1 to 5.
In the semiconductor light-emitting device according to claim 6, material systems having lattice matching with that of the GaAs substrate, such as AlGaAs, AlGaInP, ZnSe, and the like may be used.
The semiconductor light-emitting device described in claim 7 is characterized in that the plurality of reflecting multilayers, each being made from a single material system, which have a lattice constant similar to that of the semiconductor substrate, and are formed on the semiconductor substrate by using at least two material systems having a variable refractive index, comprise (AlyGa1-y)zIn1-z, P (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61); and the light-emitting layer comprises (Alyxe2x80x2Ga1-yxe2x80x2)zxe2x80x2In1-zxe2x80x2P (0xe2x89xa6yxe2x80x2xe2x89xa61, 0xe2x89xa6zxe2x80x2xe2x89xa61) in the semiconductor light-emitting device according to claim 6.
In the semiconductor light-emitting device according to claim 7, light with a wavelength ranging from red to green may be emitted by using an AlGaInP material system for the light-emitting layer and a reflecting multilayer contacting the light-emitting layer, and by varying arbitrarily the parameter sets, y and z, as well as, yxe2x80x2 and zxe2x80x2.
The semiconductor light-emitting device described in claim 8 is characterized in that the plurality of reflecting multilayers, each being made from a single material system, which have a lattice constant similar to that of the semiconductor substrate, and are formed on the semiconductor substrate by using at least two material systems having a variable refractive index, comprise AlxGa1-xAs (0xe2x89xa6xxe2x89xa61) in the semiconductor light-emitting device according to claim 7.
In the semiconductor light-emitting device according to claim 8, since the reflecting multilayer made from AlxGa1-xAs (0xe2x89xa6xxe2x89xa61) shows a higher reflectance to the light in a wavelength ranging from red to green than the reflecting multilayer made from (AlyGa1-y)zIn1-zP (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) does, a higher reflectance can be obtained with a less number of layers.
The semiconductor light-emitting device described in claim 9 is characterized in that the plurality of reflecting multilayers, each being made from a single material system, which have a lattice constant similar to that of the light-emitting layer, and are formed on the light-emitting layer by using at least two material systems having a variable refractive index, comprise AlyGa1-xAs (0xe2x89xa6xxe2x89xa61) in the semiconductor light-emitting device according to claim 8.
In the semiconductor light-emitting device according to claim 9, since the reflecting multilayer made from AlxGa1-xAs (0xe2x89xa6xxe2x89xa61) shows a higher reflectance to the light in a wavelength ranging from red to green than the reflecting multilayer made from (AlyGa1-y)zIn1-zP (0xe2x89xa6yxe2x89xa61, 0xe2x89xa6zxe2x89xa61) does, a higher reflectance can be obtained with a less number of layers.
The semiconductor light-emitting device described in claim 10 is characterized in that, in the semiconductor light-emitting device according to any one of claims 1 to 9, a distance from a boundary to the active layer is 0.3 xcexcm or longer, said boundary being between a reflecting multilayer made form the same material system as that of the uppermost reflecting multilayer of the plurality of reflecting multilayers, each being made from a single material system, which have a lattice constant similar to that of the semiconductor substrate, and are formed on the semiconductor substrate by using at least two material systems having a variable refractive index, and a reflecting multilayer provided below said reflecting multilayer and made from another material system.
In the semiconductor light-emitting device according to claim 10, since a distance from the active layer to the boundary between a reflecting multilayer made form the same material system as that of the uppermost reflecting multilayer and a reflecting multilayer made from another material system is 0.3 xcexcm or longer, an active layer having a high crystal quality can be formed.
The semiconductor light-emitting device described in claim 11 is characterized in that the active layer is a quantum-well layer in the semiconductor light-emitting device according to any one of claims 1 to 10.
In the semiconductor light-emitting device according to claim 11, since the active layer is a quantum-well, this light-emitting device can be applied to resonant-cavity LEDs, surface-emitting laser diodes, and the like, having a quantum-well active layer, to manufacture a high-efficient semiconductor light-emitting device.